A need exists for high resolution printing apparatus capable of on-line for functioning to print data which is being simultaneously displayed on a cathode ray tube or similar device, without interfering with the flow of such data. For example, such printing apparatus may be needed in bank check processing systems in which checks are displayed on cathode ray tubes to enable operators to verify signatures and/or to manually encode on the check certain information, such as the amount, which they read from the check. In certain instances, a "hard" copy may be needed of the check being displayed, with such a copy being provided by a printer coupled to the CRT.
It will be recognized that certain problems must be solved in the provision of such printing apparatus. For one thing, the electronic scanning of the check for display purposes takes place at a very high speed, while a printer is inherently a substantially slower device. For another thing, electronic scanning and reproduction of images normally uses an interlace technique, in which adjacent image scan lines are generated and reproduced in alternate scans of the image by the scanning device. Printers do not normally operate in this fashion, and accordingly, some translation or conversion of the scanned information for printing purposes is desirable.